I want to start a bunch of docker containers with a help of a Python script. I am using subprocess library for that. Essentially, I am trying to run this docker command
docker = f"docker run -it --rm {env_vars} {hashes} {results} {script} {pipeline} --name {project} {CONTAINER_NAME}"
in a new terminal window.
Popen(f'xterm -T {project} -geometry 150x30+100+350 -e {docker}', shell=True)
# or
Popen(f'xfce4-terminal -T {project} --minimize {hold} -e="{docker}"', shell=True)
Container's CMD looks like this. It's a bash script that runs other scripts and funtions in them.
CMD ["bash", "/run_pipeline.sh"]
What I am trying to do is to run an interective shell (bash) from one of these nested scripts in a specific place in case of a failure (i.e. when some condition met) to be able to investigate the problem in script, do something to fix it and continue execution (or just exit if I could not fix it).
if [ $? -ne 0 ]; then
echo Investigate manually: "$REPO_NAME"
bash
if [ $? -ne 0 ]; then exit 33; fi
fi
I want to do these fully automatically so I don't have to manually keep track of what is going on with a script and execute docker attach... when needed, because I will run multiple of such containers simultaneously.
The problem is that this "rescue" bash process exits immediately and I don't know why. I think it should be something about ttys and stuff, but I've tried bunch of fiddling around with it and had no success.
I tried different combinations of -i, -t and -d of a docker command, tried to use docker attach... right after starting container with -d and also tried starting python script directly from bash in a terminal (I am using Pycharm by default). Besides I tried to use socat, screen, script and getty commands (in nested bash script), but I don't know how to use them properly so it didn't end good as well. At this point I'm too confused to understand why it isn't working.
EDIT:
Adding minimal NOT reproducable (of what is not working) example of how I am starting a container.
# ./Dockerfile
FROM debian:bookworm-slim
SHELL ["bash", "-c"]
CMD ["bash", "/run_pipeline.sh"]
# run 'docker build -t test .'
# ./small_example.py
from subprocess import Popen
if __name__ == '__main__':
env_vars = f"-e REPO_NAME=test -e PROJECT=test_test"
script = f'-v "$(pwd)"/run_pipeline.sh:/run_pipeline.sh:ro'
docker = f"docker run -it --rm {env_vars} {script} --name test_name test"
# Popen(f'xterm -T test -geometry 150x30+100+350 +hold -e "{docker}"', shell=True).wait()
Popen(f'xfce4-terminal -T test --hold -e="{docker}"', shell=True).wait()
# ./run_pipeline.sh
# do some hard work
ls non/existent/path
if [ $? -ne 0 ]; then
echo Investigate manually: "$REPO_NAME"
bash
if [ $? -ne 0 ]; then exit 33; fi
fi
It seems like the problem can be in a run_pipeline.sh script, but I don't want to upload it here, it's a bigger mess than what I described earlier. But I will say anyway that I am trying to run this thing - https://github.com/IBM/D2A.
So I just wanted some advice on a tty stuff that I am probably missing.
Run the initial container detached, with input and a tty.
docker run -dit --rm {env_vars} {script} --name test_name test
Monitor the container logs for the output, then attach to it.
Here is a quick script example (without a tty in this case, only because of the demo using echo to input)
#!/bin/bash
docker run --name test_name -id debian \
bash -c 'echo start; sleep 10; echo "reading"; read var; echo "var=$var"'
while ! docker logs test_name | grep reading; do
sleep 3
done
echo "attach input" | docker attach test_name
The complete output after it finishes:
$ docker logs test_name
start
reading
var=attach input
The whole process would be easier to control via the Docker Python SDK rather than having a layer of shell between the python and Docker.
As I said in a comment to Matt's answer, his solution in my situation does not work either. I think it's a problem with the script that I'm running. I think it's because some of the many shell processes (https://imgur.com/a/JiPYGWd) are taking up allocated tty, but I don't know for sure.
So I came up with my own workaround. I simply block an execution of the script by creating a named pipe and then reading it.
if [ $? -ne 0 ]; then
echo Investigate _make_ manually: "$REPO_NAME"
mkfifo "/tmp/mypipe_$githash" && echo "/tmp/mypipe_$githash" && read -r res < "/tmp/mypipe_$githash"
if [ $res -ne 0 ]; then exit 33; fi
fi
Then I just launch terminal emulator and execute docker exec in it to start a new bash process. I do it with a help of Docker Python SDK by monitoring the output of a container so I know when to launch terminal.
def monitor_container_output(container):
line = b''
for log in container.logs(stream=True):
if log == b'\n':
print(line.decode())
if b'mypipe_' in line:
Popen(f'xfce4-terminal -T {container.name} -e="docker exec -it {container.name} bash"', shell=True).wait()
line = b''
continue
line += log
client = docker.from_env()
conatiner = client.containers.run(IMAGE_NAME, name=project, detach=True, stdin_open=True, tty=True,
auto_remove=True, environment=env_vars, volumes=volumes)
monitor_container_output(container)
After I finish my investigation of a problem in that new bash process, I will send "status code of investigation" to tell the script to continue running or exit.
echo 0 > "/tmp/mypipe_$githash"
I'm using a python script for send websocket notification,
as suggested here.
The script is _wsdump.py and I have a script script.sh that is:
#!/bin/sh
set -o allexport
. /root/.env set
env
python3 /utils/_wsdump.py "wss://mywebsocketserver:3000/message" -t "message" &
If I try to dockerizing this script with this Dockerfile:
FROM python:3.8-slim-buster
RUN set -xe \
pip install --upgrade pip wheel && \
pip3 install websocket-client
ENV TZ="Europe/Rome"
ADD utils/_wsdump.py /utils/_wsdump.py
ADD .env /root/.env
ADD script.sh /
ENTRYPOINT ["./script.sh"]
CMD []
I have a strange behaviour:
if I execute docker run -it --entrypoint=/bin/bash mycontainer and after that I call the script.sh everything works fine and I receive the notification.
if I run mycontainer with docker run mycontainer I see no errors but the notification doesn't arrive.
What could be the cause?
Your script doesn't launch a long-running process; it tries to start something in the background and then completes. Since the script completes, and it's the container's ENTRYPOINT, the container exits as well.
The easy fix is to remove the & from the end of the last line of the script to cause the Python process to run in the foreground, and the container will stay alive until the process completes.
There's a more general pattern of an entrypoint wrapper script that I'd recommend adopting here. If you look at your script, it does two things: (1) set up the environment, then (2) run the actual main container command. I'd suggest using the Docker CMD for that actual command
# end of Dockerfile
ENTRYPOINT ["./script.sh"]
CMD python3 /utils/_wsdump.py "wss://mywebsocketserver:3000/message" -t "message"
You can end the entrypoint script with the magic line exec "$#" to run the CMD as the actual main container process. (Technically, it replaces the current shell script with a command constructed by replaying the command-line arguments; in a Docker context the CMD is passed as arguments to the ENTRYPOINT.)
#!/bin/sh
# script.sh
# set up the environment
. /root/.env set
# run the main container command
exec "$#"
With this use you can debug the container setup by replacing the command part (only), like
docker run --rm your-image env
to print out its environment. The alternate command env will replace the Dockerfile CMD but the ENTRYPOINT will remain in place.
You install script.sh to the root dir /, but your ENTRYPOINT is defined to run the relative path ./script.sh.
Try changing ENTRYPOINT to reference the absolute path /script.sh instead.
How to control host from docker container?
For example, how to execute copied to host bash script?
This answer is just a more detailed version of Bradford Medeiros's solution, which for me as well turned out to be the best answer, so credit goes to him.
In his answer, he explains WHAT to do (named pipes) but not exactly HOW to do it.
I have to admit I didn't know what named pipes were when I read his solution. So I struggled to implement it (while it's actually very simple), but I did succeed.
So the point of my answer is just detailing the commands you need to run in order to get it working, but again, credit goes to him.
PART 1 - Testing the named pipe concept without docker
On the main host, chose the folder where you want to put your named pipe file, for instance /path/to/pipe/ and a pipe name, for instance mypipe, and then run:
mkfifo /path/to/pipe/mypipe
The pipe is created.
Type
ls -l /path/to/pipe/mypipe
And check the access rights start with "p", such as
prw-r--r-- 1 root root 0 mypipe
Now run:
tail -f /path/to/pipe/mypipe
The terminal is now waiting for data to be sent into this pipe
Now open another terminal window.
And then run:
echo "hello world" > /path/to/pipe/mypipe
Check the first terminal (the one with tail -f), it should display "hello world"
PART 2 - Run commands through the pipe
On the host container, instead of running tail -f which just outputs whatever is sent as input, run this command that will execute it as commands:
eval "$(cat /path/to/pipe/mypipe)"
Then, from the other terminal, try running:
echo "ls -l" > /path/to/pipe/mypipe
Go back to the first terminal and you should see the result of the ls -l command.
PART 3 - Make it listen forever
You may have noticed that in the previous part, right after ls -l output is displayed, it stops listening for commands.
Instead of eval "$(cat /path/to/pipe/mypipe)", run:
while true; do eval "$(cat /path/to/pipe/mypipe)"; done
(you can nohup that)
Now you can send unlimited number of commands one after the other, they will all be executed, not just the first one.
PART 4 - Make it work even when reboot happens
The only caveat is if the host has to reboot, the "while" loop will stop working.
To handle reboot, here what I've done:
Put the while true; do eval "$(cat /path/to/pipe/mypipe)"; done in a file called execpipe.sh with #!/bin/bash header
Don't forget to chmod +x it
Add it to crontab by running
crontab -e
And then adding
#reboot /path/to/execpipe.sh
At this point, test it: reboot your server, and when it's back up, echo some commands into the pipe and check if they are executed.
Of course, you aren't able to see the output of commands, so ls -l won't help, but touch somefile will help.
Another option is to modify the script to put the output in a file, such as:
while true; do eval "$(cat /path/to/pipe/mypipe)" &> /somepath/output.txt; done
Now you can run ls -l and the output (both stdout and stderr using &> in bash) should be in output.txt.
PART 5 - Make it work with docker
If you are using both docker compose and dockerfile like I do, here is what I've done:
Let's assume you want to mount the mypipe's parent folder as /hostpipe in your container
Add this:
VOLUME /hostpipe
in your dockerfile in order to create a mount point
Then add this:
volumes:
- /path/to/pipe:/hostpipe
in your docker compose file in order to mount /path/to/pipe as /hostpipe
Restart your docker containers.
PART 6 - Testing
Exec into your docker container:
docker exec -it <container> bash
Go into the mount folder and check you can see the pipe:
cd /hostpipe && ls -l
Now try running a command from within the container:
echo "touch this_file_was_created_on_main_host_from_a_container.txt" > /hostpipe/mypipe
And it should work!
WARNING: If you have an OSX (Mac OS) host and a Linux container, it won't work (explanation here https://stackoverflow.com/a/43474708/10018801 and issue here https://github.com/docker/for-mac/issues/483 ) because the pipe implementation is not the same, so what you write into the pipe from Linux can be read only by a Linux and what you write into the pipe from Mac OS can be read only by a Mac OS (this sentence might not be very accurate, but just be aware that a cross-platform issue exists).
For instance, when I run my docker setup in DEV from my Mac OS computer, the named pipe as explained above does not work. But in staging and production, I have Linux host and Linux containers, and it works perfectly.
PART 7 - Example from Node.JS container
Here is how I send a command from my Node.JS container to the main host and retrieve the output:
const pipePath = "/hostpipe/mypipe"
const outputPath = "/hostpipe/output.txt"
const commandToRun = "pwd && ls-l"
console.log("delete previous output")
if (fs.existsSync(outputPath)) fs.unlinkSync(outputPath)
console.log("writing to pipe...")
const wstream = fs.createWriteStream(pipePath)
wstream.write(commandToRun)
wstream.close()
console.log("waiting for output.txt...") //there are better ways to do that than setInterval
let timeout = 10000 //stop waiting after 10 seconds (something might be wrong)
const timeoutStart = Date.now()
const myLoop = setInterval(function () {
if (Date.now() - timeoutStart > timeout) {
clearInterval(myLoop);
console.log("timed out")
} else {
//if output.txt exists, read it
if (fs.existsSync(outputPath)) {
clearInterval(myLoop);
const data = fs.readFileSync(outputPath).toString()
if (fs.existsSync(outputPath)) fs.unlinkSync(outputPath) //delete the output file
console.log(data) //log the output of the command
}
}
}, 300);
Use a named pipe.
On the host OS, create a script to loop and read commands, and then you call eval on that.
Have the docker container read to that named pipe.
To be able to access the pipe, you need to mount it via a volume.
This is similar to the SSH mechanism (or a similar socket-based method), but restricts you properly to the host device, which is probably better. Plus you don't have to be passing around authentication information.
My only warning is to be cautious about why you are doing this. It's totally something to do if you want to create a method to self-upgrade with user input or whatever, but you probably don't want to call a command to get some config data, as the proper way would be to pass that in as args/volume into docker. Also, be cautious about the fact that you are evaling, so just give the permission model a thought.
Some of the other answers such as running a script. Under a volume won't work generically since they won't have access to the full system resources, but it might be more appropriate depending on your usage.
The solution I use is to connect to the host over SSH and execute the command like this:
ssh -l ${USERNAME} ${HOSTNAME} "${SCRIPT}"
UPDATE
As this answer keeps getting up votes, I would like to remind (and highly recommend), that the account which is being used to invoke the script should be an account with no permissions at all, but only executing that script as sudo (that can be done from sudoers file).
UPDATE: Named Pipes
The solution I suggested above was only the one I used while I was relatively new to Docker. Now in 2021 take a look on the answers that talk about Named Pipes. This seems to be a better solution.
However, nobody there mentioned anything about security. The script that will evaluate the commands sent through the pipe (the script that calls eval) must actually not use eval for the whole pipe output, but to handle specific cases and call the required commands according to the text sent, otherwise any command that can do anything can be sent through the pipe.
That REALLY depends on what you need that bash script to do!
For example, if the bash script just echoes some output, you could just do
docker run --rm -v $(pwd)/mybashscript.sh:/mybashscript.sh ubuntu bash /mybashscript.sh
Another possibility is that you want the bash script to install some software- say the script to install docker-compose. you could do something like
docker run --rm -v /usr/bin:/usr/bin --privileged -v $(pwd)/mybashscript.sh:/mybashscript.sh ubuntu bash /mybashscript.sh
But at this point you're really getting into having to know intimately what the script is doing to allow the specific permissions it needs on your host from inside the container.
My laziness led me to find the easiest solution that wasn't published as an answer here.
It is based on the great article by luc juggery.
All you need to do in order to gain a full shell to your linux host from within your docker container is:
docker run --privileged --pid=host -it alpine:3.8 \
nsenter -t 1 -m -u -n -i sh
Explanation:
--privileged : grants additional permissions to the container, it allows the container to gain access to the devices of the host (/dev)
--pid=host : allows the containers to use the processes tree of the Docker host (the VM in which the Docker daemon is running)
nsenter utility: allows to run a process in existing namespaces (the building blocks that provide isolation to containers)
nsenter (-t 1 -m -u -n -i sh) allows to run the process sh in the same isolation context as the process with PID 1.
The whole command will then provide an interactive sh shell in the VM
This setup has major security implications and should be used with cautions (if any).
Write a simple server python server listening on a port (say 8080), bind the port -p 8080:8080 with the container, make a HTTP request to localhost:8080 to ask the python server running shell scripts with popen, run a curl or writing code to make a HTTP request curl -d '{"foo":"bar"}' localhost:8080
#!/usr/bin/python
from BaseHTTPServer import BaseHTTPRequestHandler,HTTPServer
import subprocess
import json
PORT_NUMBER = 8080
# This class will handles any incoming request from
# the browser
class myHandler(BaseHTTPRequestHandler):
def do_POST(self):
content_len = int(self.headers.getheader('content-length'))
post_body = self.rfile.read(content_len)
self.send_response(200)
self.end_headers()
data = json.loads(post_body)
# Use the post data
cmd = "your shell cmd"
p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
p_status = p.wait()
(output, err) = p.communicate()
print "Command output : ", output
print "Command exit status/return code : ", p_status
self.wfile.write(cmd + "\n")
return
try:
# Create a web server and define the handler to manage the
# incoming request
server = HTTPServer(('', PORT_NUMBER), myHandler)
print 'Started httpserver on port ' , PORT_NUMBER
# Wait forever for incoming http requests
server.serve_forever()
except KeyboardInterrupt:
print '^C received, shutting down the web server'
server.socket.close()
If you are not worried about security and you're simply looking to start a docker container on the host from within another docker container like the OP, you can share the docker server running on the host with the docker container by sharing it's listen socket.
Please see https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface and see if your personal risk tolerance allows this for this particular application.
You can do this by adding the following volume args to your start command
docker run -v /var/run/docker.sock:/var/run/docker.sock ...
or by sharing /var/run/docker.sock within your docker compose file like this:
version: '3'
services:
ci:
command: ...
image: ...
volumes:
- /var/run/docker.sock:/var/run/docker.sock
When you run the docker start command within your docker container,
the docker server running on your host will see the request and provision the sibling container.
credit: http://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/
As Marcus reminds, docker is basically process isolation. Starting with docker 1.8, you can copy files both ways between the host and the container, see the doc of docker cp
https://docs.docker.com/reference/commandline/cp/
Once a file is copied, you can run it locally
docker run --detach-keys="ctrl-p" -it -v /:/mnt/rootdir --name testing busybox
# chroot /mnt/rootdir
#
I have a simple approach.
Step 1: Mount /var/run/docker.sock:/var/run/docker.sock (So you will be able to execute docker commands inside your container)
Step 2: Execute this below inside your container. The key part here is (--network host as this will execute from host context)
docker run -i --rm --network host -v /opt/test.sh:/test.sh alpine:3.7
sh /test.sh
test.sh should contain the some commands (ifconfig, netstat etc...) whatever you need.
Now you will be able to get host context output.
You can use the pipe concept, but use a file on the host and fswatch to accomplish the goal to execute a script on the host machine from a docker container. Like so (Use at your own risk):
#! /bin/bash
touch .command_pipe
chmod +x .command_pipe
# Use fswatch to execute a command on the host machine and log result
fswatch -o --event Updated .command_pipe | \
xargs -n1 -I "{}" .command_pipe >> .command_pipe_log &
docker run -it --rm \
--name alpine \
-w /home/test \
-v $PWD/.command_pipe:/dev/command_pipe \
alpine:3.7 sh
rm -rf .command_pipe
kill %1
In this example, inside the container send commands to /dev/command_pipe, like so:
/home/test # echo 'docker network create test2.network.com' > /dev/command_pipe
On the host, you can check if the network was created:
$ docker network ls | grep test2
8e029ec83afe test2.network.com bridge local
In my scenario I just ssh login the host (via host ip) within a container and then I can do anything I want to the host machine
I found answers using named pipes awesome. But I was wondering if there is a way to get the output of the executed command.
The solution is to create two named pipes:
mkfifo /path/to/pipe/exec_in
mkfifo /path/to/pipe/exec_out
Then, the solution using a loop, as suggested by #Vincent, would become:
# on the host
while true; do eval "$(cat exec_in)" > exec_out; done
And then on the docker container, we can execute the command and get the output using:
# on the container
echo "ls -l" > /path/to/pipe/exec_in
cat /path/to/pipe/exec_out
If anyone interested, my need was to use a failover IP on the host from the container, I created this simple ruby method:
def fifo_exec(cmd)
exec_in = '/path/to/pipe/exec_in'
exec_out = '/path/to/pipe/exec_out'
%x[ echo #{cmd} > #{exec_in} ]
%x[ cat #{exec_out} ]
end
# example
fifo_exec "curl https://ip4.seeip.org"
Depending on the situation, this could be a helpful resource.
This uses a job queue (Celery) that can be run on the host, commands/data could be passed to this through Redis (or rabbitmq). In the example below, this is occurring in a django application (which is commonly dockerized).
https://www.codingforentrepreneurs.com/blog/celery-redis-django/
To expand on user2915097's response:
The idea of isolation is to be able to restrict what an application/process/container (whatever your angle at this is) can do to the host system very clearly. Hence, being able to copy and execute a file would really break the whole concept.
Yes. But it's sometimes necessary.
No. That's not the case, or Docker is not the right thing to use. What you should do is declare a clear interface for what you want to do (e.g. updating a host config), and write a minimal client/server to do exactly that and nothing more. Generally, however, this doesn't seem to be very desirable. In many cases, you should simply rethink your approach and eradicate that need. Docker came into an existence when basically everything was a service that was reachable using some protocol. I can't think of any proper usecase of a Docker container getting the rights to execute arbitrary stuff on the host.
In one of the containers in Docker, it's running a flask application with API endpoints exposed. I'm trying to configure a cron by updating crontab file to consume the api on regular intervals.
Dockerfile
FROM nikolaik/python-nodejs:python3.7-nodejs14
ENV APP /deploy
.....
.......
COPY . /$APP
RUN pip install -e .
EXPOSE 8080
ADD entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT /entrypoint.sh
entrypoint.sh
#!/bin/sh
until PGPASSWORD=$POSTGRES_PASSWORD psql -h "postgres" -U "postgres" -c '\q'; do
>&2 echo "Postgres is unavailable - sleeping"
sleep 1
done
>&2 echo " "
/venv/bin/uwsgi app.ini
# Setup a cron schedule
>&2 echo "* * * * * /usr/bin/curl -X GET http://localhost:8080/import_data >/var/log/stdout1.log 2>/var/log/stderr1.log
# This extra line makes it a valid cron" > scheduler.txt
crontab scheduler.txt
cron -f
on executing the command
docker-compose up
There are no updates done to scheduler.txt. I checked the container and none of the files which created from these -scheduler, stdout, stderr . Above postgres operations work while below print statements are also not executed.
Alternatively, This can be done by using a different container for cron and creating a virtual network for these two containers but i want to understand what's going wrong when try to update in same container.
Let me know if more info is required on same.
My guess would be that you did not delete the container instances and used:
docker compose stop
instead of
docker compose down
In that case the container will only be stopped and not removed. when then running the compose up command the containers will simpy be restarted and not rebuild/recreated. Note that things that happen inside of the Dockerfile will only be running/changing when first creating the container (assuming that the image was correctly updated).
On your second note I would add that that would be a better solution in my humble opinion. A docker container is typically meant to only do 1 thing. So if this container is running a service and exposing endpoints a second container would be consuming said endpoints on an interval. This separation of functionality is quite easy to setup and makes it clearer which container is in charge of what.
Is it possible to run a python script automatically upon starting a Docker container?
My command to attach to an image is:
docker run -i -t --entrypoint /bin/bash myimage -s
Is there a way to add an additional command that runs a script upon launching it?
I would prefer not to use a Dockerfile as some of the python modules I use are from private repos and need to be downloaded manually, so a Dockerfile would not completely build the image I want.
As a matter of fact there is. Just don't use --entrypoint. Instead:
docker run -it myimage /bin/bash -c /run.sh
Obviously, this assumes that the image itself contains a simple Bash script at the location /run.sh.
#!/bin/bash
command1
command2
command3
...
If you don't want that, you can mount the current folder inside the running container and run a local script:
docker run -it -v $(pwd):/mnt myimage /bin/bash -c /mnt/run.sh
ENTRYPOINT vs. CMD seems to be a common cause of confusion.
Think about it this way:
ENTRYPOINT is a way to hard-code a certain behavior that cannot be changed after setting it up.
CMD is the default way to supply a command to be run.
Docker containers can be set up to run as self-contained applications. If you're so inclined, you could create throwaway containers that accept command line arguments (a file for example), pull that in, work their magic and return you a processed file. Some people use this to set up build environments with different configurations and just run them on demand, not cluttering up their host machine.
However, your usage scenario feels tedious, since you are apparently doing the setup by hand. It would be easier to set the download credentials as environment variables, like this:
docker run -d -e "DEEP=purple" -e "LED=zeppelin" myimage /bin/bash -c /run.sh
You can then use those within the script as placeholders. This way, you get the best of both worlds. For added security, your run.sh should unset the environment variables once they have been used, like this:
#!/bin/bash
command1
command2
command3
...
unset DEEP
unset LED